A rodent discovered last year in Laos may actually be a survivor of a group believed to have been extinct for 11 million years, an international group of scientists reported on Thursday.
The squirrel-like animal, called Laonastes aenigmamus, was interpreted as the sole member of a new family, Laonastidae, when scientists first witnessed its skeleton in 2005. It looks apparently different from other living rodents.
But now, a team of US, French and Chinese researchers said it belongs to the family of Diatomyidae, an extinct early rodent that lived from early Oligocene to late Miocene in Asia.
By comparing the similarities of teeth, mandible, dentition, vertebrae and head between the Lao rodent and the Diatomyidae fossil, researchers concluded that the squirrel-like animal should be a direct descendant of the Diatomyidae found in Shandong Province, China.
The team led by Mary Dawson at the Carnegie Museum of Natural History published its findings in the March 10 issue of the journal Science. Chuan-kui Li, a researcher at the Chinese Academy of Sciences, is also a member of the team.
"Our phylogenetic analysis of morphological data from various living and extinct rodents identifies Laonastes as a member of Diatomyidae, being more closely related to Diatomys (found in Shandong)," the researchers wrote in the Science paper. "We therefore synonymize Laonastidae with Diatomyidae."
The discovery of the living diatomyid rodent Laonastes offers a rare case of the so-called "Lazarus effect," which refers to the re-appearance of a species after a lengthy blank in the fossil record, the researchers said.
"Uniquely among placental mammals, Laonastes pertains to a clade (Diatomyidae) that was formerly believed to have been extinct for more than 11 million years," they wrote in the paper.
"Diatomyids join tree shrews, flying lemurs, and tarsiers as examples of ancient and formerly widerranging mammalian taxa that are currently living with relictual distributions in southeast Asia."
Such a phenomenon shows that Southeast Asia's prehistoric "zoo" can offer invaluable insights regarding past and present biodiversity.
"If it can be preserved, the Paleogene zoo that survives today in southeast Asia can offer invaluable insights regarding past and present biodiversity," the scientists said.
"Efforts to conserve Laonastes, the sole survivor of a morphologically distinctive family of rodents with deep evolutionary roots in Asia, should be given the highest priority," they wrote.
(Xinhua News Agency March 11, 2006)
